1. Field of the Invention
The present invention relates to a balancer apparatus of an engine having a balance weight rotated in cooperation with a crankshaft for canceling an inertia force accompanied by reciprocal movement of a piston.
2. Description of Related Art
There is known an engine for a motorcycle, for example, containing a balancer apparatus for canceling an inertia force of a reciprocal movement portion of a piston, a connecting rod or the like inside of a crank case.
A balancer apparatus of this kind includes a balance weight rotated at a speed the same as that of the crankshaft and in a direction inverse thereto. There is a mode of the balance weight installed on the crankshaft coaxially therewith and another mode thereof installed on a shaft separate from the crankshaft, and in either of the cases, the balance weight is driven by transmitting power from the crankshaft.
A conventional balancer apparatus includes a pair of balance weights and the balance weights are respectively supported rotatably on journal portions disposed at both ends of the crankshaft. The balance weights need to rotate in a direction inverse to that of the crankshaft and therefore, a middle shaft is arranged in parallel with the crankshaft. The middle shaft includes a pair of sprockets rotating at a speed the same as that of the crankshaft and in a direction inverse thereto at both ends thereof and chains are hung between the sprockets and the balance weights.
Therefore, an output outputted to the crankshaft is temporarily transmitted to the sprockets on the intermediate shaft and thereafter transmitted to the balance weights via the chains.
When the balance weights are coaxially installed on the crankshaft, there is needed the exclusive middle shaft for driving the balance weights in the direction inverse to that of the crankshaft. Therefore, there is a drawback that the number of shafts is increased and the crank case supporting shafts becomes large-sized.
Further, since the balance weights are disposed at the journal portions at both ends of the crankshaft, when, for example, an output is outputted from a shaft end of the crankshaft by utilizing a gear, the gear cannot be disposed proximate to a center portion of the crankshaft along an axial direction due to a hindrance by the balance weights or the chains.
As a result, the gear for outputting the output is considerably extended to an outer side in the axial direction of the crankshaft to cause to bring about a large-size formation of the crank case. Along therewith, in outputting the output from the shaft end of the crankshaft, there poses a problem that a path of outputting the output becomes complicated, or the output is difficult to be outputted.
On the other hand, according to another conventional balancer apparatus, a balance weight is disposed on a main shaft of a transmission or a balancer shaft. The main shaft or the balancer shaft is disposed in parallel with the crankshaft and disposed on an outer side of a rotational locus drawn by an outer peripheral face of a crank web to avoid interference of the crankshaft with the crank web.
However, according to the constitution, spaces for bringing in the crank web need to be ensured between the crankshaft and the main shaft as well as between the crankshaft and the balancer shaft, and it is unavoidable that a distance between the shafts is increased. As a result, the crank case becomes large-sized and the balance weight cannot compactly be integrated to the crank case.
It is an advantage of the invention to provide a balancer apparatus of an engine capable of compactly integrating a balance weight to a crank case and capable of preventing a large-size formation of the crank case.